1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a thin film transistor (TFT) including a selectively crystallized channel layer and a method of manufacturing the TFT.
2. Description of the Related Art
TFTs are used for static random access memories (SRAMs) and read only memories (ROMs). Particularly, TFTs are widely used as pixel driving devices in active matrix flat panel displays. For example, TFTs are used as switching devices or current driving devices in liquid crystal displays or organic electro-luminescence displays.
When TFTs are used as switching devices, the TFTs protect pixels from electric interferences with neighboring pixels and transmit electric signals to the pixels.
TFTs are formed of a semiconductor such as amorphous silicon (Si) and poly-Si. Poly-Si may be a suitable semiconductor for forming TFTs in terms of the current driving ability and charge carrier mobility of the TFTs. However, amorphous Si may be more suitable for forming TFTs when process temperature and available substrates are considered. Therefore, most of the current TFTs are formed using amorphous Si.
However, when amorphous Si is used for forming channel layers of TFTs, the charge carrier mobility of the channel layers is low (0.5 cm2/Vs). Therefore, it is difficult to increase the operating speed of a liquid crystal display when TFTs having amorphous-Si channel layers are used as switching devices in a liquid crystal display.
For this reason, ZnO based materials such as Ga—In—Zn—O having a higher charge carrier mobility than amorphous Si have been studied as materials for channel layers of TFTs